1. Field of Invention
The invention relates to an electrophotographic lamination film having an image formed (recorded) directly with an image-forming device in an electrophotographic system, and in particular to an electrophotographic lamination film used in non-contact or contact type information media containing personal information and images, such as cash cards, employee identification cards, student identification cards, membership cards, resident identification cards, various kinds of driver's licenses and various kinds of certificates containing face photographs, and sheets with images for identification, image displaying plates and indication labels used in the medical field etc.
2. Description of Related Art
As image-forming techniques have been developed in recent years, a method of forming images having identical qualities inexpensively in large amounts by various printing methods such as intaglio printing, letterpress printing, planographic printing, gravure printing and screen printing is known. Such printing methods are used often in printing of the surface of information media capable of storing predetermined information and communicating with external devices contacting or not contacting therewith, such as IC cards, magnetic cards, optical cards, and cards as a combination thereof.
However, the screen printing requires many printing plates in accordance with the number of images to be printed, and color printing requires additional printing plates in accordance with the number of colors. Accordingly, these printing methods are not suitable for dealing with information for personal identification (face photograph, name, address, date of birth, various kinds of licenses).
To solve the problem, image-forming means used mainly at present is a method of forming an image with e.g. a printer in a sublimation-type or fusion-type thermal transfer system using an ink ribbon etc. The method can easily print information for personal identification, but there remain problems such as lower resolution at a higher printing speed and a lower printing speed in higher resolution.
On the other hand, formation (printing) of an image in the electrophotographic system is conducted by charging the surface of an image carrier uniformly and exposing it to light depending on an image signal, to form an electrostatic latent image by a potential difference between a light-exposed portion and a non-exposed portion, followed by electrostatic development of a color powder (image forming material) called as a toner having polarity opposite to (or identical with) the charge thereby forming a visualized image (toner image) on the surface of the image carrier. In the case of color images, the process is repeatedly carried out or a plurality of image-forming devices are arranged thereby forming visible color images which are then transferred and fixed (fixing by mainly thermally melting and cooling the color powder) to an image recording material to give color images.
As described above, the electrostatic latent image on the surface of the image carrier is electrically formed using an image signal in the electrophotographic system, thus permitting not only the same image to be repeatedly formed but also different image to be easily formed. Further, the toner image on the surface of the image carrier can be transferred almost completely to the surface of the image recording material, and the toner image slightly remaining on the surface of the image carrier can be easily removed by a resin blade or a blush, and thus printed materials can be produced easily in a small number of different forms.
The toner is formed usually by melt-mixing additives such as hot-melt resin, a pigment and if necessary a charging regulator and pulverizing the mixture through milling. As compared with the pulverized toner, the electrostatic latent image in the electrophotographic system has sufficiently high resolution, and can be expected to have sufficiently higher resolution than in screen printing or in the thermal transfer system using an ink ribbon.
With respect to color images, the color toner has four primary colors of cyan, magenta, yellow and black, and by mixing these colors, any colors theoretically identical to those in printing can be realized. Further, the color toner can be relatively freely blended with a toner resin and a pigment, and thus the shielding of an image by the toner can be easily increased.
There is no or less examination of heat resistance and light resistance assuming that the image-recording material is used outdoors, but when driver's licenses etc. are placed particularly under sunrays in cars, thermal transfer-type images using dyes as coloring matter are faded. In the output of color images in the electrophotographic system, however, pigments excellent in light resistance, corresponding to the respective colors of cyan, magenta, yellow and black, are used in the color toner, so the image recording material in the electrophotographic system can be expected to be highly light resistant. When a heat-resistant toner is selected, the image recording material can also be endowed with heat resistance to such an extent as to be usable outdoors.
On the other hand, the substrate (core) in various cards used widely at present is a vinyl chloride sheet because it is excellent not only in printing characteristics but also in embossing processability (treatment of making letters etc. uneven). However, the vinyl chloride sheet has a problem of generation of dioxin by combustion in a heating oven upon disposal after use, and from an environmental point of view, various kinds of sheet films came to be used as those free of vinyl chloride.
Assuming that embossing is not conducted, preexisting biaxially oriented PET (polyethylene terephthalate) film or the like can be used. However, embossing is often indispensable for keeping the functions of cards, and at present, ABS resin film softening at a relatively low temperature, polyolefin resin film, modified PET resin film called PETG, or a film where modified PET resin film and PET film or amorphous PET resin film or polycarbonate resin film have been integrally molded, came to be used.
Examples of printing on various kinds of cards using the above-described electrophotographic device are as follows:
For example, Japanese Patent Application Laid-Open (JP-A No.) No. 2001-92255 discloses a method in which invisible bar codes in addition to various kinds of personal information are printed on a vinyl chloride sheet of 250 μm in thickness or a polyester sheet of 280 μm in thickness by an electrophotographic method, and an over-film is layered on the printed surface and laminated by a heat pressing machine.
However, the above-described sheets have a high coefficient of friction so that they adhere to each other to deteriorate sheet transferability to stop the electrophotographic device, while the above-described insulating material (sheet) of 250 μm or more in thickness is liable to increase image defects because of insufficient transfer of an image forming material (toner) thereto. Further, when the resin film softening at a relatively low temperature is used for printing with an electrophotographic device, the film is made viscous because the fixing temperature of the toner in the fixing step is higher than the softening temperature of the resin, thus causing a problem of sticking of the film to the fixing device to generate jams. Further, the image forming material causes offset in the fixing device, and when fixation of the above sheet of 250 μm in thickness is continued, the fixing device may be damaged considerably by the edge (corner) of the sheet.
Further, JP-A No. 11-334265 describes that a light-permeable sheet is printed with a mirror image of information for personal identification. With respect to the light-permeable laminated sheet, however, it is merely described that a part of the laminated sheet is preferably a biaxially oriented polyester film or a film made of ABS or polyester/biaxially oriented polyester film, but may be vinyl chloride.
However, the film according to JP-A No. 11-334265 supra is merely an insulating material to undergo insufficient transfer of the image forming material to the surface of the film, thus failing to achieve the same resolution as in the thermal transfer system. Further, the laminated sheet used in the device emphasizing improvements in productivity is in a rolled shape, so there is a problem of much loss and iste in the case of emergent production or in production of many kinds of cards, for example in printing of different cards for one to several persons.